Spatial and temporal patterns of mineralization rates and oxygen distribution in a permeable intertidal sand flat (Sylt, Germany)

Abstract

Oxygen distribution and benthic mineralization rates were investigated in a permeable intertidal sand flat (permeability: 3.9 3 10 211 m 2 ) in a transect from the low toward the high waterline. At all stations, oxygen penetrated several millimeters to centimeters into the sediments during inundation because of pore-water advection. The wave-and current-driven deep oxygen penetration caused high oxygen consumption rates (OCRs) and high aerobic mineralization rates at all stations. Because oxygen penetration was enhanced during inundation, 71-90% of the daily oxygen consumption took place in that period. OCRs and sulfate reduction rates (SRRs) changed with inundation time of the stations, emphasizing the importance of pore-water advection for benthic mineralization: OCRs were elevated at the lower flat in summer (lower flat 131-187; middle and upper flat 64-108 mmol C m 22 d 21 ). SRRs increased sharply from the high to the low waterline during all seasons (e.g., in summer: lower flat 18-40; middle flat 8.8-9.4, upper flat 0.5-4 mmol C m 22 d 21 ). A one-dimensional model of the advective organic matter supply to the sediment could only explain a fraction of the organic carbon required for benthic mineralization. This suggests that either transport of particles via the seawater is more efficient than the one-dimensional concept can explain or that additional carbon was supplied through other sources (e.g., benthic photosynthesis). Mineralization rates were higher in summer than in winter. Only in summer did sulfate reduction contribute .20% to total mineralization.

The drivers of biogeochemistry in beach ecosystems: A cross-shore transect from the dunes to the low-water line

“…, which is even higher than the rate determined for comparable shallow subtidal or intertidal sands (Rusch et al, 2006;Werner et al, 2006). The presence of NO 2 − at site 2 is also indicative of changing redox conditions because it is either released when NH 4 + is oxidized via nitrification when encountering aerobic conditions (Kowalchuk et al, 1997) or when NO 3 − is transformed to N 2 via denitrification under anaerobic conditions (Evrard et al, 2013;Slomp and Van Cappellen, 2004).…”

Bioturbation and bioirrigation extend the open exchange regions in permeable sediments

“…Sediments at the study site are moderately sorted fine sand with a median particle size of 230 mm. Additional investigations were done at a nearby (2 km) subtidal site with an advective-driven permeable sand, composed of moderately well-to well-sorted medium sand with a median grain size of 340 mm Werner et al 2006). Salinity at all sites varies on average between 27.5 in spring and 31 in summer, and freshwater upwelling is negligible.…”

“…7B). The temporal variability of the areal OCR at the lugworm site indicates a higher susceptibility to physical and biological advection, resulting in dynamic oxygen penetration during inundation (Werner et al 2006). Table 3.…”

“…The supply of oxygen to the sediment regulates the distribution of microbial communities (Fenchel and Finlay 1995) and, in turn, organic matter degradation and nutrient cycling (Mackin and Swyder 1989). Despite the low organic content, conversion rates in permeable sand can be high due to efficient input of oxygen and organic matter, and removal of degradation products (Werner et al 2006).…”

Marine Phytophthora species can hamper conservation and restoration of vegetated coastal ecosystems

“…Every experimental unit was equipped with a separate pump for aeration to prevent cross-infection among experimental units. This system was sufficient to aerate the entire water column, which is representative of the Wadden Sea winter conditions [34]. Treatments were randomly assigned to the experimental units.…”